Nonregenerative radio circuits



Nov. 25,2 1930. o. KNIGHT v 7 ;9

NONREGENERATIVE RADIO CIRCUITS Filed April 17, 1924 Patented Nov. 25, 1 930 i N menmnmm name CIRCUITS;

Applicatien filed. April 17,

L aThisinyention relates in general to audion circuits l as used, for example, in radio communication and other electrical arts in which atigrid Forv control electrode governs the "flow bfelectron-current from a heated filament nor icathode to a plate ;or anode. A primary objectoflthe invention is to ,control the re- 7 generative tendency of audion tubes or circuits byreducing the effect of electrostatic M coupling ,hetvveen grid and plate electrodes Aand preventgeneration of oscillations.

is adapted and: applied, the: electrostatic ca pacity hetweeii iplalte and-grid electrodes (to- M1 lgether withtheir respective leads) gives rise to ajtransferof plate circuit .energyto the grid circuit: when aachainge in the strength of the platecunrent occurs, and when this "energy transfer occurs in proper phaserelal tion'livitha changein gridpotential, the ef-' feet will be to add- :to; the change of 'gridtpo- ='tential1and give rise to the familiar negeneraati-ve action within-:the-audion and its circuits. f Theleffect is ls'lubject, of course, to: quantitawtive considerations involving the constants of :the-cinciiits, thewdesign of the audion, and

the-frequency or rapidity a-t W-hi'ch the change' in gridzi potential Occurs; In; general, it is :favored :by ilOWQ resistance, high electrode ca- 1v r'pacity, and high frequency; These factors maybe such astopermit thesystem to act as an? independent generator ,of oscillating current, Whichof-ten is detrimental'to the pura,

pose intended. :For example, the employy jment of tuned I radio frequency amplif er stages in radio receivers isoften accompanied by considerahle diiiicultydue to the tendency 1 of the system to generate oscillations 'when i l f; the {circuits I are tuned to approximate resonance, and thisytendency maybe such as to preyenttthe designing of the receiver on the jmmost efficient lines.

of reducing or substantially eliminating the,

1 upling le tw enml e a d g i i e t y erpes n bet t se i ts n ucet eim an e By; slee n t mi sd me in ,the gridfreturn lead, which .is hereunder 'e eqil a h th l adb t een th fil me a amplifier stage,

1924; wSerial no. 707;150."

proper flow ofgplat'e lc'urreiit throughthe tOry circuit the filament circuit, the

plate filament circuit is'in no way interrupt- 7 ed. Likewise the grid,being a voltage operatedelement, may continue to perform its normal :funct on Without mpairment, pro- The nature of the invent on ing diagrams illustrating the-use ofthe iny any V understood with reference to the accompany: l I "In many of the uses to which theaudion L vention in various circuits While the. in-

Vention is notlimited to the radio art, We may assume for the sake of clearness, that these c rcuit diagrams,represent certa in standard radlo clrcult s lniconimon usetoday, wltflthe impedance element I inserted for, controlling the regenerative tendency of thefaudion f I Figure a diagra Figure Qrepresents H,

Figure 3 showsfaTreceiyer system inclu ding .one stage'oftuned rad o frequency a nplifi- I cation a; tuneddetectonfand one or more ,stages lof ,audio frequency amplificationf Referringin detail to Figure 1 ofthe 'dralwi ting, 10'indieatesthegrid, 11 the plate and 12:

of an nntuned radio 'frequency amplifierfs'tagej i '3 atuned radio frequency 77 l the' filament o'fanaudion'f primary coil 13' of a radiofrequency transformer is located in the plate circuit and connected by conduct 1 6 t plus side 91 batt ry 7 t negative terminal 'of which is connected to the plus side of thejAt-battery lfi. The filament 12 is connected conductor17 Withthe plus terminalof A-battery 16 and minus terminal" of B t-battery 15, thus completingthe plate p l filament cirlcuiflQArheOstat 18 isconnected with theother terminalof filament 12 and throug'htthe arm19;is cionnectedwith the minus terminal o f"the'A battery 16.1 The :ondary coil 21 of a coupling transformer, the

lower'terminal f which is connectd by con- *filanient systemiis thus completed. The grid ,ductor 22=with one -endjof an inductive 'impedanceele nent 23,"whose otheri endfis;coneased, ibmemlaabrfii ith thamlgias terms mo I nal of the A-battery 16. This completes the grid filament system. The conductors 23 and 24 here constitute the grid return lead. Coil 21 represents, by way of example, an element in the grid filament circuit, by which voltage variations are imparted to the grid electrode. The impedance 23 is an inductive impedance and is thus conductive to direct current. Its value will depend upon the extent to which it is desired to limit the electrostatic coupling effect existing between grid 10 and plate 11 of the audion for the particular system in which it is employed. The function of the impedance may be clearly understood on the theory that an electrostatic influence of the plate potential upon the grid potential depends upon the transfer of electrons from plate to grid or vice versa and that the extent to which this transfer may occur is dependent partly upon the impedance which the electrons encounter in their travel through, what may be termed, the plate grid circuit. It will be noted that this circuit is normally completed through the unobstructed junction between plate-filament system and gridfilament system, but that in accordance with the present invention, the high frequency transfer of electrons is impeded by the high inductive reactance of the element 23, which does not, however, interfere with the normal current in the platefilament circuit or the proper voltage variation in the grid circuit. As an inductive reactance or impedance element, I have found satisfactory, an iron cored choke coil comprising in the neighborhood of one thousand to fourteen hundred turns of about No. 30 enameled wire upon a soft iron core onequarter of an inch in diameter and about one inch in length occupied by the turns.

The impedance element 23 should not be of such value or connected in such manner as to have any substantial effect in causing a departure of the grid potential from the desired normal value. At higher frequencies a higherimpedance is necessary on account of the smaller capacitative impedance of the grid and plate electrodes in the tube. By the use of an inductive impedance, the opposition to regeneration automatically increases at the higher frequencies. In the design of the inductive impedance, care must naturally be exercised in avoiding undue distributed capacity so that within the frequencies contemplated, the impedance will retain a sufficient preponderance of inductive reactance.

From the above general description of the nature and function of the impedance 23, its use in other types of circuits will be readily understood. 7

Referring to Figure 2, the circuit is substantially the same as that shown in Figure l, with the exception that here the secondary coil 21 has the tuning capacity or condenser 25 connected in parallel therewith forming a closed oscillatory circuit, to one side of which the grid electrode 10 is connected and to the other side of which the impedance 23 is connected, the conductor 24 constituting the grid return lead from the closed oscillatory circuit 21, 25 to the negative terminal of the A-battery, and having inserted therein the impedance 23 as before. The voltage oscillation in the closed oscillatory circuit 21, 25 is not opposed by the impedance 23, as the latter is outside of the closed circuit, but the normal functions of the audion occur without the usual tendency to regenerate and produce oscillations.

Figure 3 illustrates in principle the application of the invention to a receiving set employing radio frequency amplification, a tube detector, and audio frequency amplification. In this case the antenna inductance is coupled with the inductance 21, across which is the tuning capacity 25, to one side of which the grid 61 is connected and to the other side of which the choke coil 23 is connected. Choke coil 23 is here again interposed in the connection from the closed oscillatory circuit of the grid which leads to the negative lead 62 of the A-battery 63. The detector circuit is illustrated as comprising the closed oscillatory circuits 64, 65, grid condenser 66, grid leak 67, grid 68 and grid return lead 69 to the filament 70. The output from plate 71 passes through primary 72 of an audio frequency transformer, whose secondary 73 is connected to the grid 74 of the audio amplifier tube. Detector B-battery lead 75 connects the primary coil 72 with the B-battery 76 at the desired tap, the negative terminal of the B-battery being connected to the plus terminal of the A-battery. The various battery leads and circuit connections are of standard present-day practice and need not be specifically described. The use of the impedance 23 interposed in the grid return lead enables the radio frequency amplifier to be tuned to maximum amplification without fear of oscillation occurring from the interelectrode capacity of the grid and plate elements. The detector'tube being ordinarily operated on much lower voltage than that of the amplifier tubes and having the output connected through an untuned audio frequency transformer, will not ordinarily require the use of the impedance 23, although, of course, the same may be employed in the detector circuit, if desired.

The above description with reference to a number of different examples of the use of the invention will enable those skilled in this artto understand and practice the invention. No attempt has been made to illustrate all of the great variety of circuits in which the impedance element 23 may be used to advantage. The value of the impedance referred to may be varied to meet different requirements, but the values which I have given above, by way of example, have been found in practice to be suflicient to'prevent the generation of oscillations in the audion tube and its associated circuits, in the case of high vacuum tubes of relatively high internal plate grid capacity, such as those marketed under the, designationxUV20l-A Radiotron. Such tubes have been successfully employed in all of the circuits illustrated'and in similar circuitsin which a plurality of stages of radio frequency amplification were utilized. V a

I claim 2- A radio frequency amplifier circuit comprising an audion with input and output circuits tending to produce regeneration through theplategrid capacity ofthe audion, said input circuit having connected between grid and filament a variable radio frequency tuning circuit comprising an inductance element shunted by a condenser, for imparting at variable radio frequencies a voltage between grid andfilar'nent, and a chokec'oil interposed in the connection of the filament to said tuning circuit, the inductive reactance of said choke coil sufiicientlypredominating, at the a radio frequencies to which said tuning circuit maybe tuned, to substantially checkthe feed back of radiofrequency energy from the output circuit to the input circuit through the plate-grid capacity. 7

p OCTAVIUS KNIGHT. y 

